Organic rubbers with mercaptoorganosiloxanes having improved elongation



United States Patent 3,382,196 ORGANIC RUBBERS WETH MERCAPTOOR- GANOSILOXANES HAVEN G IMPROVED ELONGATION William G. gGowdy and Joseph W. Keil, Midland, Mich, assignors to Dow Corning Corporation, Midland, Mich, a corporation of Michigan No Drawing. Filed June 3, 1965, Ser. No. 461,157 6 Claims. (Cl. 2603) This application relates to silicone-modified organic elastomers that possess improved elongation without a major loss in tensile strength or toughness.

Elastomers of high elongation are known, but high elongation has typically required a low crosslink density in the elastomer, which results in low tensile strength.

The elastomers of this invention possess a unique combination of properties. These elastomers are intimatelymixed compositions consisting essentially of (1) 100 parts by weight of a nonsiliceous organic elastomer stock which is heat vulcanizable through aliphatically unsaturated groups, and (2) from 1 to 5 parts by weight of an organosilicon compound consisting essentially of (a) (R SiO) units and at least two (b) (HSRSiO units, said (b) units being separated from each other by an average of at least (a) units, Where R is a monovalent hydrocarbon or halohydrocarbon radical, free of aliphatic unsaturation, R is a divalent hydrocarbon radical, free of aliphatic unsaturation, and n has a value of O to 2.

Ingredient (1) can be any organic elastomer stock which is not a silicone elastomer stock, and which is vulcanizable through aliphatically unsaturated groups. A good test of the above is whether or not the stock can be vulcanized with sulfur, which is a well-known technique for vulcanizing organic polymers that contain aliphatic unsaturation. Examples of useable polymers are those shown in Example 1, plus polychloroprene and polybutadiene.

The rubber stocks which are useful as ingredient (1) must be vulcanizable. Therefore, sulfur, an organic peroxide, or some other vulcanizing agent must be present in the stock. It is furthermore desirable for a filler to be present, examples of which are silica, carbon black, glass fibers, alumina, or titania. Many varieties of vulcanizable rubber stocks are commercially available.

Other ingredients can be added to the rubber stock as desired. Many potential additives are known to those skilled in the art, e.g. zinc oxide, stearic acid, coumeroneindene resin, glycerine, and other commercial additives.

Ingredient (2) is a copolymer of mercaptoorganosiloxane and diorganosiloxane units as described above.

R can be any monovalent hydrocarbon radical which is free of aliphatic unsaturation, e.g. alkyl and cycloalkyl radicals such as methyl, ethyl, propyl, isohexyl, octadecyl, and cyclohexyl; and aryl-containing radicals such as phenyl, 2-phenylpropyl, tolyl, xenyl and naphthyl.

R can also be any monovalent halohydrocarbon radical which is free of aliphatic unsaturation, c.g. haloalkyl and cycloalkyl radicals such as 3,3,3-trifluoropropyl, 4- chlorooctyl, 1,1,2,2-tetrahydrofiuorooctyl, and bromocyclopentyl'; and halogenated aryl-containing radicals such ice as dibromophenyl, u,a,u-trifluorotolyl, fluorobenzyl, and trichloroxenyl.

R can be any divalent hydrocarbon radical which is free of aliphatic unsaturation, e.g. methylene, propylene, isobutylene hexamethylene, octadecamethylene,

l Oom, 4110-, and OHZZHOCHF Small amounts of other groups can be present in ingredient (b), for example, silicon-bonded hydroxyl groups, silicon-bonded hydrolyzable groups such as Cl, OCHg, GC2H5, and

it OGCHa and siloxane units such as RSiO and R SiO Where R is defined above.

It is preferred for ingredient (2) to be a mercaptoendblocked composition of the formula r HSR SiO SiRSH R mR where in has an average value of 10 to 150, and the other symbols are defined above.

It is particularly preferred for ingredient (2) to be of the formula t t IISR SIiO S|iRSH R mR where R is a divalent alkyl radical and in has an average value of 10 to 100.

The compositions of this invention are best mixed by milling, which is the standard method for preparing rubber stocks.

The best vulcanization times and temperatures of the compositions of this invention do not differ significantly from those of the corresponding silicone-free rubber stocks. Vulcanization temperatures generally run from to 200 C., and the vulcanization time generally runs from 10 minutes to 1 hour.

The following examples are illustrative only and should not be construed as limiting the invention, which is properly delineated in the appended claims.

EXAMPLE 1 Samples of organic rubber stocks consisting essentially of 100 parts by weight of the polymers shown below, from 40 to 60 parts of finelydivided silica, from 2.5 to 5 parts of zinc oxide, from 1.5 to 6 parts of sulfur, and from 0.5 to 2 parts of stearic acid were compounded on a hot (200 F.) two-roll mill and vulcanized for 45 minutes at C. and 5000 psi.

Identical samples to the above were milled until homogeneous on a hot (200 F.) two-roll mill with 3 Weight percent, based on the weight of the rubber stock, of an organosilicon compound of the formula:

CH CH is milled at 100 C. and vulcanized for 15 minutes at 175 C., a cured elastomer having improved elongation is produced.

I I EXAMPLE 4 s H H HSCm s10 10 2S 5 When 50 g. of polychloroprene (a polymer of CH3 -19 CH: CH CClCH=CH having a viscosity of 52 cs. at 25 C. These samples were 2- 2) cured as above. 20 g. of carbon black, 2 g. of sulfur, and 2 g. of an or- The physical properties of these samples were tested 1 ganosilicon compound of the formula, and found to be as follows: CH

01 a on; Tensile Elongation Rubber Stock Duromstrength, to break I (HSCHzCEhCHzSiO 1/2);

eter lb./sq. in. point siom CH2 (percent) CH;

15 CH OF 30 (a) {Natural 81 2, 060 510 Natura with l 89 1,840 (500 is milled at 120 C. and vulcanized for 15 minutes at 3,260 510 200 C., a cured elastomer having improved elongation i i i ii 'i n so 3 200 (no is produced 0 0 6X3 19110 \V1 S1160 e 4 Styrene-butadiene and 2() EXAMPLE 5 polybutadiene 87 2, 515 520 ygf g a ggag g gfi When 50 g. of poly(ethylac rylate), 5 g. of polyisoprene, g g 83 2,950 650 g. of glass fibers, 2 g. of dicumyl peroxide, and 3 g. of Butadiene-aerylonitrile (high nitrile content) 97 3, 550 285 02H CH3 (d) Butadiene-aerylonitrile 9 I (high nitrile content) (CHzCHCH2)a s/ S10 2)zS with silicone 9s 3, 500 345 Butadiene-acrylonitrile CH3 CH; to CH3 3 (low nitrile content) 83 3, 860 400 (e) .f'fi 1s milled at 150 C. and vulcanized at 175 C. for g;;g; {,,g?f f 91 3,250 490 minutes, a cured elastomer having improved elongation gug in n nn 2g 8 38 is produced. stnltuii%%?:,- s4 2,i0 500 That h h is claim?! is: (s)- y e W101 1. An intimately mixed composition consisting essensiheone 83 3,010 660 c tially or (1) 100 parts by weight of a nonsiliceous organic EXAMPLE 2 elastomer stock which is heat-vulcanizable through (a) A composition consisting of g. of a styreneallphfltlcally unsaturated p nd butadiene rubber base, 20 g. of powdered silica having a from 1 t0 5 P by welght of an organosilicon surface area of about 270 square meters per gram, 2.5 compound consisting essentially of g. of zinc oxide, 0.15 g. of sulfur, 0.5 g. of magnesium (a) (R 810) units, and at least two stearate, and 1.35 g. of dicumyl peroxide was rolled on a 40 hot (200 F.) 2-rol1 mill for 15 minutes. The composi- Hswsio tion was then cured for 15 minutes at 320 F. 1 t2) units (b) A composition consisting of 100 parts by Weight 2 of (a) above and 3 parts of said (b) units bein separated from each other by an average of at least 10 (a) units, HSOmCHCHQ sio SiCmCHOmSH where R 15 a monovalent hydrocarbon or halohydrocarbon radlcal, free of aliphatic unsatura CH3 CH3 CH3 CH5 tion, R is a divalent hydrocarbon radical, free having a viscosity at 25 C. of 440 cs. was milled and 0 of aliphatic unsaturation, and n has a value of cured as above. 0 0 to 2.

The physical properties of the two cured rubbers were 2. The cured composition of claim 1. as above: 3. The composition of claim 1 where (2) is of the formula Tensile Elongation to Rubber Durometer strength break point R R IG/sq. in. (percent) l IISR SiO SiRSI'I s3 1, 030 79 990 35 R m R EXAMPLE 3 where R is a niono valent hydrocarbon or lialoh d (30 bon, free of aliphatic unsaturatlon, R is a divalent hydro- When 50 g. of polybutacliene, 15 g. of carbon black, carbon radical, free of aliphatic unsaturation, and 111 has 2 g. of sulfur, and 2.5 g. or an organosilicon compound an average value of at least 10. of the formula 4. The cured composition of claim 3.

3)3 l0l/2]2 HS- CH2S1O S10 CH3 1O 6 (iHSH 5 6 5. The composition of claim 1 where (2) is of the 6. The cured composition of claim 5. formula CH3 CH3 References Cited L E UNITED STATES PATENTS CH3 m g 5 2,867,603 1/1959 Safford et a1 260-827 where R" is a divalent alkyl radical, and m! has an aver- SAMUEL BLECH, primary Examinen age value of from 10 to 100. 

1. AN INTIMATELY MIXED COMPOSITION CONSISTING ESSENTIALLY OF (1) 100 PARTS BY WEIGHT OF A NONSILICEOUS ORGANIC ELASTOMER STOCK WHICH IS HEAT-VALCANIZABLE THROUGH ALIPHATICALLY UNSATURATED GROUPS, AND (2) FROM 1 TO 5 PART BY WEIGHT OF AN ORGANOSILICON COMPOUND CONSISTING ESSENTIALLY OF (A) (R2SIO) UNITS, AND AT LEAST TWO (B) 